The present invention relates to a crimp terminal for connecting electric wires by crimping, and more particularly to an improvement of conductor engaging grooves (serrations) which are formed on an inner face of a bottom plate part, etc. of the terminal, and advantageously contribute to an improvement of electrical connecting performance as well as an improvement of mechanical connecting performance between the terminal and conductors of the electric wires.
FIGS. 6 and 7 show examples of related-art crimp terminals.
A crimp terminal 1 as shown in FIG. 6 is the crimp terminal for screw fitting, and includes a terminal portion 2 for screw fitting which has a screw insertion hole 2a formed at its distal end, a conductor crimping portion 4 and a sheath crimping portion 5 which are provided in order behind the terminal portion 2. These portions are integrally formed of a sheet of metal plate by stamping process.
The conductor crimping portion 4 is a portion for connecting bare conductors 7b by crimping, which are exposed by removing an insulation sheath 7a from a sheathed electric wire 7, as also shown in FIG. 8. The conductor crimping portion 4 has a bottom plate part 4a on which the bare conductors 7b are placed, and a pair of crimp claws 4b which are adapted to be crimped onto the bare conductors 7b placed on this bottom plate part 4a, by a crimping equipment 9 (See FIG. 9).
The sheath crimping portion 5 is a portion for crimping the sheathed electric wire 7 to fix it together with the insulation sheath 7a, and includes a bottom plate part 5a on which the sheathed electric wire 7 is placed, and a pair of crimp claws 5b which are crimped onto the sheathed electric wire 7 placed on the bottom plate part 5a, by the crimping equipment 9 (See FIG. 9).
The crimping equipment 9 is a kind of pressing apparatus which includes, as shown in FIGS. 9 and 10, an anvil 9a for supporting the bottom plate parts 4a, 5a of the conductor crimping portion 4 and the sheath crimping portion 5, and two crimpers 9b, 9c provided above the anvil 9a so as to move up and down for respectively crimping the crimp claws 4b and the crimp claws 5b. 
Meanwhile, a crimp terminal 11 as shown in FIG. 7, is a relaying crimp terminal for connecting conductors of a plurality of sheathed electric wires 12a, 12b, 12c together in a bundle, and has a bottom plate part 11a on which a plurality of bare conductors 13 are placed, and a pair of crimp claws 11b which are extended from both sides of the bottom plate part 11a and adapted to be crimped onto the bare conductors 13 placed on the bottom plate part 11a, by a crimping equipment. The bottom plate part 11a and the crimp claws 11b are integrally formed of a sheet of metal plate by stamping process.
It has been known that in order to enhance electrical connecting performance and mechanical connecting performance between the bare conductors and the bottom plate parts of these crimp terminals, a plurality of conductor engaging grooves 17 in a concave shape (hereinafter referred to as xe2x80x9cserrationsxe2x80x9d) extending in a direction intersecting axes of the bare conductors (usually, in a perpendicular direction) are provided on an inner face 16 of the bottom plate part, etc. of the terminal to be contacted with the bare conductors, as shown in FIGS. 11 and 12.
In this case, all the serrations have a groove width and a groove depth of the same size, and are in the same shape.
When the crimp claws 4b, 11b have been crimped, groove edges of the serrations 17 are intensively pressed so as to adequately bite the bare conductors 7b, 13 on the surface, and both the mechanical connecting performance and the electrical connecting performance can be improved, ensuring reliability of the connection by crimping.
By the way, in order that oxidized coatings formed by oxidation on the surfaces of the conductors may be removed when the edges of the serrations 17 have bitten the bare conductors 7b, 13 by the edges, it is necessary for the serrations 17 to be set to have a large amount of bite, and it is necessary to make the serrations 17 deep for an increase of the amount of bite.
On the other hand, in case where the serrations have been set to have a large amount of bite, stresses will be converged on crimped areas of the conductors when a tensile force is exerted on the bare conductors 7b, 13 from outside. As the results, the bare conductors 7b, 13 will be likely to be broken, resulting in deterioration of the mechanical connecting performance.
Under the circumstances, in order that improvements of the electrical connecting performance and the mechanical connecting performance may be obtained while keeping their balance, the depth of the serrations 17 and crimping amounts of the crimp claws can be determined in consideration of outer diameters of the bare conductors.
However, there have been many cases in which the crimp terminals employed in a wire harness or the like for a motor vehicle must connect the sheathed electric wires having various diameters, or must crimp the conductors having different outer diameters together in a bundle.
For this reason, it is extremely difficult to determine the depth of the serrations 17 and the crimping amounts of the crimp claws so that improvements of both the electrical connecting performance and the mechanical connecting performance can be obtained while keeping their balance. For example, in case where a plurality of the bare conductors having different outer diameters have been crimped together in a bundle, even though the large diametered bare conductors may be improved both in the electrical connecting performance and the mechanical connecting performance, the small diametered bare conductors may be too much engaged by the serrations 17, resulting in a probability that even a slight tensile force may break the bare conductors.
Moreover, in case where the mechanical connecting performance is intended to be ensured, by setting the depth of the serrations 17 according to the bare conductor having the smallest diameter among the bare conductors 7b, 13 to be crimped, there has been such an anxiety that in the bare conductors having the larger diameters, the edges of the grooves cannot sufficiently remove the oxidized coatings on the surfaces of the conductors, incurring defective electrical connecting performance.
In order to eliminate such disadvantages contradicting each other, a crimp terminal 21 as shown in FIGS. 13 and 14 has been proposed.
This crimp terminal 21 is disclosed in Japanese Patent Publication No. JP 59-165390A, and includes two conductor crimping portions 23, 24 having different crimping amounts. The conductor crimping portion 23 positioned at a proximal end side of the bare conductors forms a crimping part having a small amount of bite of the serrations with respect to the conductors, by adjusting a height of the crimp claws 23b, 23b and controlling a crimper 26b in a crimping equipment 26 so as to obtain a smaller crimping amount.
On the other hand, the conductor crimping portion 24 which is positioned at a distal end side of the bare conductors forms a crimping part having a large amount of bite of the serrations with respect to the conductors, by adjusting a height of the crimp claws 24b, 24b and controlling a crimper 26c in the crimping equipment 26 so as to obtain a larger crimping amount.
In this manner, by providing two types of the conductor crimping portions 23, 24 having different crimping amounts, incomplete or excessive amount of bite by the serrations has been eliminated, even in case where the bare conductors having small diameters and large diameters are mixed, and both the electrical connecting performance and the mechanical connecting performance have been able to be improved.
However, in the crimp terminal 21 as shown in FIGS. 13 and 14, an increase in number of the conductor crimping portions 23, 24 has incurred a problem that a structure of the terminal has become complicated and large-sized. In addition, the crimping equipment 26 has become also complicated due to an addition of the crimper 26c, and there has arisen a problem that cost for the equipment might be increased.
It is therefore an object of the invention to provide a crimp terminal in which, on occasion of crimping operation when the bare conductors of both small diameters and large diameters are mixed, an excessive or incomplete bite in any conductor can be eliminated, without incurring a complicated and large-sized structure of the crimp terminal, and also without incurring a complicated crimping equipment, and both electrical connecting performance and mechanical connecting performance can be improved at a low cost.
In order to achieve the above object, according to the present invention, there is provided a crimp terminal for crimping at least one bare conductor of at least one sheathed electric wire, comprising:
a bottom plate, on which the at least one bare conductor is placed;
a pair of crimp craws, extending from the bottom plate to crimp the at least one bare conductor placed on the bottom plate; and
a plurality of serrations formed at least on an inner face of the bottom plate to bite the at least one bare conductor crimped by the crimp claws,
wherein at least one of the serrations has a depth different from a depth of each another serration.
In this construction, when the crimping operation is performed, the shallow serration will prevent an excessive bite thereby to attain improvement of the mechanical connecting performance, and on the other hand, the deep serration will prevent the oxidized coating from remaining due to an incomplete bite thereby to attain improvement of the electrical connecting performance.
Further, the serrations having different depths can ensure appropriate amounts of bite with respect to both the bare conductors having a small diameter and a large diameter, although no additional crimping structure is required.
Therefore, on occasion of crimping operation when the bare conductors having both a small diameter and a large diameter are mixed, an excessive or incomplete bite with respect to either conductor can be eliminated, without incurring a complicated and large-sized structure of the crimp terminal, and also without incurring a complicated crimping equipment, and both the electrical connecting performance and the mechanical connecting performance can be improved at a low cost.
Preferably, a depth of a serration situated closer to an end of the bottom plate at which the sheathed electric wire is placed is shallower than a depth of another serration.
When plural sheathed electric wires are placed at both ends of the bottom plate, it is preferable that depths of serration closer to the both ends of the bottom plate are shallower than a depth of another serration.
In these cases, it is possible to decrease an amount of bite between the serrations and the bare conductors at the proximal end side of the bare conductors, so that deterioration of the mechanical connecting performance due to an excessive bite can be reliably prevented.
Preferably, a depth of a center portion of the at least one serration in an extending direction thereof is shallower than depths of both end portions thereof.